1. Field of the Invention
The present invention pertains to an oscillating signal light mechanism which mechanically produces cycles of substantially constant velocity arc segment oscillations of one or more signal light assemblies.
2. Description of the Related Art
Signal light mechanisms of the type provided by the present invention are primarily employed on emergency and service vehicles such as police cars, fire department vehicles and road maintenance trucks. Similar mechanisms have also been employed in flashing light assemblies of other types of vehicles and in other applications where it is desired to attract the attention of individuals to flashing light signals from considerable distances.
It has long been recognized that attracting the attention of individuals to the presence of a light signal is more efficiently attained using a flashing light rather than a steady burning light. It is also generally known that flashing lights are generated more efficiently through mechanical motion of a reflector or lens assembly positioned adjacent a steady burning light rather than through electrical current interruption of a light filament. For many years signal light assemblies employing a reflector rotated about a light filament of the assembly, commonly referred to as a rotating beacon, have served as a practical means of providing visual warning.
A rotating beacon generates a beam signal of essentially constant flash rate and intensity through the entire 360.degree. viewing area of rotation of the beam. However, in order for the beam signal generated by the rotating beacon to be visible in all directions around the beacon, the rotating beacon cannot be used in situations where the rotating beam signal will be obstructed. For example, when employed on vehicles the rotating beacon is typically mounted on the top most portion of the vehicle to avoid the rotating beam of the beacon from being obstructed by any portion of the vehicle. However, many emergency vehicles have a physical size or shape that prevents the rotating beam of a beacon from being seen. To overcome this problem, a multiple of rotating beacon light assemblies are typically installed on a vehicle so that, in combination, the assemblies provide the required visibility of flashing light signals from all points around the vehicle perimeter.
However, mounting a multiple of rotating beacon signal light assemblies on a vehicle requires a substantial amount of energy to operate the multiple assemblies. Moreover, that portion of the signal light of each rotating beacon assembly that is obstructed by a portion of the vehicle serves no signalling purpose and is wasted. To overcome this problem, oscillating signal light assemblies have been developed which employ mirrors or reflectors that are oscillated through arc segments that are only a fraction of the signal light perimeter instead of rotating the reflector and the reflected beam through complete 360.degree. rotations.
For emergency or service vehicle applications, standards have been developed for signal light performance. These standards call for a minimum level of flash energy or intensity, in combination with a minimum and maximum number of flashes per minute visible to a stationary observer of the signal. The optimum situation to comply with the standards is to have a signal light that sweeps through a large arc to be visible around a large portion of the vehicle's perimeter, where the light signal swept through the arc has a high level of flash energy or flash intensity that is visible at a high frequency or flashes per minute to an observer positioned stationary along the swept arc.
Prior art signalling devices have been found to be disadvantaged in the size of the arc swept through by the signalling device. Typically, prior art signalling devices have been limited to angular coverage of about 130.degree., and have different angular velocities in different portions of their sweep through the arc. The flash energy or intensity of a signal light to a stationary observer increases as the illumination provided by the light filament increases, but reciprocally decreases as the angular velocity of the light beam swept through the arc increases. Thus, because the intensity of a signal light is a function of the angular velocity, the visible warning signal produced by the light is weaker in the areas of its arc sweep of high oscillation speed, and is higher in the areas of slow speeds. Studies of oscillating beacon signal lights indicate that an ideal signal light for use on emergency vehicles would be one which provides about 180.degree. of light beam sweep coverage, at essentially a constant signal flash energy, produced by a constant angular velocity of the signal light beam through the arc sweep of the beam.
Prior art signalling light apparatus have been developed that are capable of sweeping a light signal beam through an arc segment at substantially a constant angular velocity. However, these types of signalling apparatus have required involved electronic circuitry to produce the oscillating sweep of the signal light beam where the circuitry employed in the apparatus significantly increases the overall cost of producing the apparatus.